SOMETIMES a face is enough to sear a movie into your consciousness for good. As the title character in "Maria Full of Grace," Catalina Sandino Moreno is a Colombian Mona Lisa, a delicate, unforgettable force majeure. Add to her luminous demeanor a story that rips fleshy holes through your heart and you've got yourself a stunner of a film.

Maria Alvarez, 17, is convinced this life shouldn't be hers. She works in a flower plantation in Colombia, stripping the thorns from roses, one nervous eye on her relentless supervisor. It's tough work, and she doesn't take orders well. No matter how hard she works, the money never seems to be enough for her family, a tense home full of complainers, including her sister and child, her mother and grandmother. And then there's Juan (Wilson Guerrero), her good-looking but nonchalant boyfriend, who doesn't seem to appreciate her. When she tells Juan she's pregnant, his immediate request to get married is dutiful rather than romantically enthusiastic.

She rejects his robotic proposal. She quits that job. If this were a musical, and if "Maria" weren't so deadly serious, she might burst into song about a better life, like Belle in "Beauty and the Beast" or Dorothy in "The Wizard of Oz." But the texture of this movie is darker and, ultimately, scarier. Maria will get the opportunity she craves, but it's going to be the most harrowing test of her life.

Javier (Jaime Osorio Gomez) is a shaggy bear of a man, the kind of person whose gravelly sweetness could easily turn into ferocity. He offers Maria the chance of a lifetime: to swallow rubber-wrapped pellets of heroin and transport them into the United States. He's asking her to be a mule.

There is no room for failure. A successful mule makes it through, dispels her cargo, spends a week in the United States and gets her money for the delivery. But if she fails, there is no one to save her. And should one of those bags burst -- the female mules carry anywhere from 50 to 70 of these rubber pellets in their stomachs -- there's a different resolution to their worries.

This, then, is Maria's only alternative to an unfulfilling, poor life.

A character named Maria? Carrying an unborn baby? A Maria who removes thorns? Let the religious allusions apply wherever you want them to. Writer-director Joshua Marston has clearly made a modern allegory. The people she meets along her way are various moral archetypes: good, bad, ugly. They're there to test her. And she'll meet others like her, people like the nervous Lucy (Guilied Lopez) and her friend Blanca (Yenny Paola Vega), who are making the same trip, putting their bodies and lives at risk.

Maria seems to prevail through difficulties and setbacks others couldn't, thanks to her pluckiness and inviolable serenity. Even the tough ones, the battle-scarred characters who will stand before her, threaten her life, instinctively understand this. She's a cut above.

From the very beginning, Marston's movie, which has swept a path of success through the Sundance and Berlin festivals, holds us tightly in its grip. This is a cold-fever ordeal, not only for Maria but us, as pressures worsen, as the going gets sordid and dangerous. We think about the vulnerable inner structure of women's bodies, the fragile life inside Maria's womb. We face customs officers who have seen other mules trying the same thing. We see sweat on female foreheads, and we can almost feel the cold, clammy skin. We hear the heavy breathing of fear. We make this journey, too. And if there's anyone to help us go through this white-knuckle trip, it's Maria.